Many forms of electrical load powering apparatus have a load connection, a voltage supply connection and a common, and electronic circuitry which switches the voltage supply connection to an electrical load. Without limiting the intended scope of applications of the invention, the background of the invention is discussed in regard to a relatively specific example of powering electronically commutated motors for domestic appliances such as laundry apparatus.
While conventional brush-commutated DC motors may have numerous advantageous characteristics such as convenience of changing operational speeds and direction of rotation, it is believed that there may be disadvantages, such as brush wear, electrical noise, and radio frequency interference caused by sparking between the brushes and the segmented commutator, that may limit the applicability of such brush commutated DC motors in some fields such as the domestic appliance field including the laundry apparatus field. Electronically commutated motors, such as brushless DC motors and permanent magnet motors with electronic commutation, have now been developed and generally are believed to have the above discussed advantageous characteristics of the brush-commutated DC motors without many of the disadvantages thereof while also having other important advantages. Such electronically commutated motors are disclosed in the David M. Erdman U.S. Pat. Nos. 4,005,347 and 4,169,990 and Floyd H. Wright U.S. Pat. No. 4,162,435, all of which are commonly assigned with the present application and are hereby incorporated by reference. These electronically commutated motors may be advantageously employed in many different fields or motor applications among which are domestic appliances, e.g., automatic washing or laundry machines such as disclosed in commonly assigned, co-pending U.S. patent application Ser. No. 412,421 filed Aug. 2 filed Apr. 13, 1982, now U.S. Pat. No. 4,449,079 Ser. No. 367,951, filed Apr. 13, 1982 now U.S. Pat No. 4,528,485; Ser. No. 400,319 filed July 21, 1982; Ser. No. 191,056 filed Sept. 25, 1980, now U.S. Pat. No. 4,459,519; Ser. No. 141,268 filed Apr. 17, 1980 now U.S. Pat. No. 4,390,826 Ser. No. 077,784 filed Sept. 21, 1979 now U.S. Pat. No. 4,327,302 and Ser. No. 463,147 filed Feb. 2, 1983 which are hereby incorporated by reference.
Laundry machines as disclosed in the above patent applications are believed to have many significant advantages over the prior art laundry machines which employ various types of transmissions and mechanisms to convert rotary motion into oscillatory motion to selectively actuate the machine in its agitation washing mode and in its spin extraction mode. Such prior art laundry machines are believed to be more costly and more complicated to manufacture, consume more energy, and require more servicing. Laundry machines with electronically commutated motors require no mechanical means to convert unidirectional rotary motion into oscillatory action for washing agitation, and in some applications, it is believed that the spin basket may be directly driven by such a motor. While the past control systems, such as those disclosed in the aforementioned coassigned applications for instance, undoubtedly illustrated many features, it is believed that the control circuits for electronically commutated motors in general, and for such motors utilized in laundry machines, could be improved, as well as the methods of control utilized therein.
Coassigned U.S. Pat. No. 4,250,544, "Combination Microprocessor and Discrete Element Control System for a Clock Rate Controlled Electronically Commutated Motor" issued Feb. 10, 1981, to R. P. Alley discloses an arrangement for controlling an electronically commutated motor and is hereby incorporated by reference. Switching of the terminals of winding stages of an electronically commutated motor is accomplished by field effect transistors therein. While such circuitry is effective and satisfactory, it is desirable in some applications contemplated for the electronic commutated motors to switch relatively high voltages including voltages from generally about 100 volts, for example, up to about 400 volts or more to the winding stages. The terminals thus undergo relatively sudden high voltage excursions relative to the common, or ground connection of the electrical load powering apparatus. Such voltages are high enough to make the inherent or stray capacitances of circuits for controlling the switching an important consideration. Moreover, in such circuits for controlling the switching which have an active device such as a junction transistor or field effect transistor, such capacitances can be multiplied by the gain of the active device in an electronic effect sometimes known as the Miller effect. It is believed that when such higher voltages are used, or whenever the inherent capacitance is significant, the probability of false triggering, lack of reliable or positive switching, and even oscillation is increased.